The invention relates to a clamp and in particular to a coupling clamp for connecting objects such as pipes, tubing, ferrules etc.
Pipe coupling clamps are extensively used in industry, particularly in the food processing, chemical and pharmaceutical sectors. The requirements of these industries demand high levels of cleanliness and the ability to sterilise pipe installations which are typically made of stainless steel.
Typical pipe installations employ pipe coupling clamps to connect open ends of lengths of pipe. Normally, a clamp liner is installed about the open end of each of the open ends to be connected. Such a clamp liner has a radially projecting flange with a coupling surface distal from the pipe open end for mating with a coupling surface of the flange of a second clamp liner. A recess for receiving a gasket is provided in the coupling surface. In order to connect the pipe lengths, the coupling surfaces of the flanges with the gasket placed therebetween are placed together, and an annular coupling clamp is secured over the flanges to hold the flanges and the gasket in a sealed relationship. Such a coupling clamp has a recess formed in its inner surface for receiving the flanges. Outer faces of the flanges distal from the coupling surfaces taper towards their peripheral regions and when the clamp is installed, tapering walls of the inner surface which define the recess abut the outer faces.
The clamp liner and gasket design are specified in British Standard, BS 4825: Part 3: 1991, International Standard, ISO 2852: 1993(E) and German Standards DIN 32676 and DIN 11864/3. The coupling clamp used to hold the clamp liners and the gasket together is not specified in any of the standards, however in both standards a sample representation of a coupling clamp is shown. The purpose of showing a representation of a coupling clamp in these standards is to indicate clearance values at the interface between outer faces of the flanges and contact faces of the side limbs of the recess of the coupling clamp. Thus the standards illustrate a profile for the recess of the coupling clamp and this profile has been adopted as an industry standard, although only certain portions of recess profile are standardized. Such a profile of the recess, however, has not been optimised in most of commercially available coupling clamps and variations of the profile in different designs of coupling clamps give rise to unsatisfactory abutment at the interface of the recess and the clamp liners i.e. such clamps do not engage the clamp liners in a manner sufficient to establish and maintain a fluid-tight seal between coupling surfaces of flanges of the clamp liners and a sealing gasket placed therebetween and, as a consequence, fluid-tightness and cleanliness of pipe connection may be compromised.
A clamp having an “omega”-profile of the internal recess is supplied by Advanced Couplings Limited, a British company, for coupling ferrules. Side walls of the recess are arcuate and thus enable linear circumferential contact of the side walls with outer faces of the ferrules. This configuration does not depend on fluctuations of angular tolerances of the outer faces of the ferrules. The disadvantage of the linear contact is that concentrated forces acting on the ferrules result in increased stresses applied at the contact interface. Furthermore such an arrangement is not suitable for increased fluctuations of thickness of the ferrule assembly, as it often occurs with modern assemblies.